President heads to Mississippi to campaign for the Republican senator facing a run-off election against Democrat challenger Mike Espy; Jonathan Serrie reports from Jackson on the campaign.

Republican Sen. Cindy Hyde-Smith appeared poised for an easy runoff against her Democratic challenger after the first round of voting in Mississippi's special election earlier this month.

But after a series of high-profile controversies, Hyde-Smith – who was appointed in March to fill the Senate seat vacated by Thad Cochran – is locked in a contentious fight with Democrat Mike Espy in what has become the most competitive Senate race the state has seen in decades.

The incumbent remains the favorite in this deep-red state that President Trump, who is stumping for Hyde-Smith in back-to-back rallies Monday evening, won by 18 points in 2016. With the runoff set for Tuesday, most analysts and political operatives on both sides of the aisle are predicting that Hyde-Smith will squeak out a win.

But her controversies have cracked open the door just a bit for Espy, even if a Democratic win in the state remains a longshot.

“Mike Espy has some momentum and Cindy Hyde-Smith has given him some freebies with her comments,” Marvin King, a political science professor at the University of Mississippi, told Fox News. “But it will change nothing overall.”

Mike Espy, a former congressman and former U.S. agriculture secretary, speaks at the Neshoba County Fair, one of the state's largest political events, in Philadelphia, Miss. Espy is challenging Sen. Cindy Hyde-Smith in a run off election for a seat in the U.S. Senate. (AP Photo/Rogelio V. Solis, File)

Hyde-Smith and Espy beat out two other candidates earlier this month, but neither was able to accumulate more than 50 percent of the vote to win the race outright -- forcing a runoff. The Nov. 6 results were surprisingly close. While polling had shown Hyde-Smith enjoying a sizeable lead over her three challengers, she garnered only 41.4 percent of the vote to Espy's 40.7 percent.

As with any runoff, the key factor will be turnout -- specifically, whether supporters of conservative candidate Chris McDaniel, who got just over 16 percent on Nov. 6, will back Hyde-Smith on Tuesday.

The controversies may boost turnout for Espy, but McDaniel's supporters, even a fraction of them, would help Hyde-Smith overcome that challenge.

“A lot of McDaniel’s supporters are going to stay home, but not a critical mass of them to change the election results,” King predicted.

Still, the controversies made the race more competitive than Republicans would have liked.

First came a video that showed the senator saying that if she were invited by one of her supporters to a "public hanging," she would be in "the front row.” The came another where she is heard telling a group of supporters that “there's a lot of liberal folks in those other schools who that maybe we don't want to vote. Maybe we want to make it just a little more difficult. So, I think that's a great idea.”

While her campaign has said her comments were "an exaggerated expression of regard” and “all a joke,” both have upset many in a state known for its history of lynchings and other racially motivated attacks on African-Americans. Mississippi also has the highest percentage of black residents – at 37 percent – and community leaders have heavily criticized the senator for her comments.

“Hyde-Smith’s decision to joke about ‘hanging,’ in a state known for its violent and terroristic history toward African Americans is sick," NAACP President Derrick Johnson said in a statement.

Hyde-Smith’s comments gave Espy – who is African-American – an opening to rally the state’s African-American community to the ballot box. Espy hopes to use those voters, along with any crossover Republicans put off by the comment, to have a shot at the seat.

"Here's what you're not going to get from me: You're not going to hear any talk about voter suppression. You're not going to hear any talk about public hanging," Espy said.

The “public hanging” comment also caused numerous big-dollar donors to ask for refunds from the Hyde-Smith campaign. Walmart, Boston Scientific, Union Pacific and Major League Baseball have all asked Hyde-Smith to return their donations.

“Sen. Hyde-Smith’s recent comments clearly do not reflect the values of our company and associates,” Walmart said in a statement posted on Twitter. “As a result, we are withdrawing our support and requesting a refund of all campaign donations.”

Espy, however, is not without controversy.

The former Mississippi congressman faces ethical questions over his work for a company that paid $2.5 million to settle a lawsuit concerning bribing of officials in a bid to score lucrative contracts with the state prison. Espy declared in his latest financial disclosure nearly $10,000 income from Global Tel Link, a controversial prison phone company.

Espy, who served as President Bill Clinton’s Secretary of Agriculture, also was paid $750,000 in 2011 to lobby for then Ivory Coast president Laurent Gbagbo’s government.

The Senate candidate has denied that he collected the full amount for lobbying for the African despot currently on trial for crimes against humanity at the International Criminal Court. A FARA Supplemental Statement filed with the Department of Justice in 2011, however, revealed that Espy not only collected the full $750,000 figure, but also dropped the contract just 15 days before it was supposed to end, instead of after a month as he claimed.

Republican operatives appear confident that Hyde-Smith will pull out a victory on Tuesday, eager to avoid another situation like last year's Alabama special election -- where Democrat Doug Jones defeated scandal-plagued Republican Roy Moore to fill the seat vacated by former Attorney General Jeff Sessions.

“I think Espy supporters are probably a little more energized than Hyde-Smith,” Henry Barbour, the Republican National Committee committeeman and a longtime Mississippi operative, told Politico. “But I do think conservative voters realize this race is going to decide if we have a conservative or liberal representing us in Washington and that is very motivating to conservative voters."

Barbour added: “We don't want to have an Alabama.”

In order to prevent that, Republicans are throwing the full weight of the party behind Hyde-Smith. Trump announced his back-to-back rallies over the weekend.

“I will be in Gulfport and Tupelo, Mississippi, on Monday night doing two Rallies for Senator Hyde-Smith, who has a very important Election on Tuesday,” Trump tweeted. “She is an outstanding person who is strong on the Border, Crime, Military, our great Vets, Healthcare & the 2nd A. Needed in D.C.”

The RNC also has more than 100 paid staff members on the ground as of this weekend, and has made more than 500,000 voter contacts in Mississippi since Nov. 6. Hyde-Smith also quickly received the endorsement of McDaniel, and her campaign hopes to draw in his supporters.